NEW YORK — Junichi Tazawa gave up a late go-ahead hit to Lyle Overbay on a split that wasn't exactly splitting.

The righty reliever allowed two runs while retiring just two of the five batters he faced in a six-run bottom of the seventh for the Yankees. Boston won 9-8 in 10 innings, but trailed 8-7 following Overbay's knock.

The progression for Tazawa: single on a fastball to Alfonso Soriano, double on a splitter to Curtis Granderson, strikeout of Alex Rodriguez on a splitter, Overbay's single on another split.

Tazawa's struggles aren't limited to just Thursday night of late, even though his overall numbers on the season are still very strong. He's allowed a combined four earned runs in his last six outings starting on Aug. 20, a four-inning span.

"It's the split more than anything," Farrell said. "Cause the power's there, the strike-throwing ability is there. All the things are there. He's using his curveball a little bit more. But the base hit to Overbay was a split that didn't really have the bottoming-out action. While you might say the bottom line hasn't been there, it's a matter of just getting a little bit consistency with the one pitch because everything else is still as strong as he's been all year."

"I think at times he's overthrowing it, and maybe the girp becomes a little bit too tense where it's not allowing the bottom-out action. We've got to look at some things and address it."

The splitter's struggles were easier to see live and on video Thursday night than they are in the numbers on the season.

The numbers, which rely on a pitch classification system, show that Tazawa has actually been better of late with the split-finger. Considerably better. But maybe a first-half problem is rearing its head again.

Tazawa's four-seam fastball's been good for a .489 slugging percentage in the second half, and a .289 average. That's a contrast to the .136 slugging against the split.

At 27, Tazawa is still something of an unknown quantity. He was excellent in 2012, but this is his first full-length season in the majors. The first half brought an easier time escaping jams for Tazawa, with 25 percent (4-of-16) of his inherited runners scoring. That's up to 43.8 percent in the second half (7-of-16).

"We're gonna need him to be as he's been for the majority of the season," Farrell said. "Lately, it's been hit and miss somewhat. Again, go back to the inconsistency of the split, that's the one pitch we got to get right for him."

Notable: as a whole in the second half, the Red Sox bullpen has allowed the third-most inherited runners to score, percentage-wise: 37.8. In terms of total inherited runners let in, the Red Sox lead the majors since the All-Star break, with 28.